Affinity MS is being used extensively in a detailed series of studies concerning proteolytic degradation of P-amyloid protein AD). In particular, the new approach is being used to help: Identify proteolytic fragments of AD in cultured cells. Measure degradation rates for AD 1 -40 and A P 1 -42. Characterize proteolytic enzymes involved in AD degradation. Examine pH dependency of proteolytic degradation of AD. Correlate proteolytic AD degradation and AD peptide composition in Alzheimer's disease patient's brain.